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| Different Types of Artificial Satellites and their Orbits |
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| The main satellite orbits around the earth are: |
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 Low earth orbit |
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 Polar orbit |
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 Elliptical orbit |
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 Geostationary orbit |
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| Low Earth Orbit |
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| Low earth orbit lies in the equatorial plane just lying above the atmosphere a few hundred miles up. |
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| Geostationary Orbit |
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| Geostationary orbit lies in the equatorial plane around 36,000 km above the equator. Any satellite launched in this orbit are made to revolve earth with a time period of 24 hours so that the satellite appears stationary with respect to a particular place on earth. |
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| Polar Orbit |
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| Polar orbits are used to watch the earth. They are the planes perpendicular to equatorial plane.
Satellites in polar orbit are low enough to collect the information about earth in detail. |
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| Low earth orbit is the easiest and cheapest to reach, lying just above the atmosphere a few hundred miles up. This is the orbit that is taken by the space shuttle, the Mir space station and the Hubble Space Telescope. |
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| Polar orbit is good for watching the earth. It is low enough to see in detail and as the earth rotates beneath each orbit surveys a new track. Polar orbit is used by Land satellites and ERS-1 (Earth Resource Satellite). |
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| Geostationary orbit, around 36,000 km above the equator lies in the equatorial plane. Any satellite put in this orbit is made to have a time period of 24 hours so that the satellite looks stationary as seen from the earth. |
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| The earth is ringed by a cosmic necklace of satellites watching over it from a range of different orbits. |
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| Satellites are of many types depending on their function. There are weather satellites which monitor wind speed, cloud temperature and height, sea temperature, etc. This data helps to predict climate changes. Spy satellites use powerful telescopes to watch for potential threats. There are also Remote Sensing Satellites. Remote sensing refers to collection of information about an object. Remote sensing satellites use sun-synchronous orbits. In these orbits the position of the sun with respect to a point on the earth remains approximately the same as the satellite passes over it. The space shuttles sometimes carries remote sensing instruments to monitor earth. The cameras fitted in the satellites scan the earth, both in visible light and infrared radiations and take photographs. ERS satellites use radar, ultraviolet and infrared
radiations to monitor the earth. Two combined images show the movement of the earth. |
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| Most of the satellites are used for
scientific research. The first satellites launched by USSR and USA were scientific. Then there are communication satellites which are used for relaying television broadcasts or telephone signals. |
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